Objectives Night shift work has been suggested as a possible risk factor for multiple sclerosis (MS). The objective of the present analysis was to prospectively evaluate the association of rotating night shift work history and MS risk in two female cohorts, the Nurses’ Health Study (NHS) and NHSII.
Methods A total of 83 992 (NHS) and 114 427 (NHSII) women were included in this analysis. We documented 579 (109 in NHS and 470 in NHSII) incident physician-confirmed MS cases (moderate and definite diagnosis), including 407 definite MS cases. The history (cumulative years) of rotating night shifts (≥3 nights/month) was assessed at baseline and updated throughout follow-up. Cox proportional hazards models were used to estimate HRs and 95% CIs for the association between rotating night shift work and MS risk adjusting for potential confounders.
Results We observed no association between history of rotating night shift work and MS risk in NHS (1–9 years: HR 1.03, 95% CI 0.69 to 1.54; 10+ years: 1.15, 0.62 to 2.15) and NHSII (1–9 years: HR 0.90, 95% CI 0.74 to 1.09; 10+ years: 1.03, 0.72 to 1.49). In NHSII, rotating night shift work history of 20+ years was significantly associated with MS risk, when restricting to definite MS cases (1–9 years: HR 0.88, 95% CI 0.70 to 1.11; 10–19 years: 0.98, 0.62 to 1.55; 20+ years: 2.62, 1.06 to 6.46).
Conclusions Overall, we found no association between rotating night shift work history and MS risk in these two large cohorts of nurses. In NHSII, shift work history of 20 or more years was associated with an increased risk of definite MS diagnosis.
- night shift work
- shift work
- circadian disruption
- multiple sclerosis
- cohort study
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Contributors KP and JM: statistical analysis, interpretation of data and paper writing. ED: interpretation of data and critical revision of the manuscript. KLM, TC, AA and ESS: study concept and design, data acquisition and critical revision of the manuscript.
Funding The study is supported by the US National Institutes of Health (Grants: T32 HL007575, UM1 CA186107, UM1 CA176726 and R01NS046635).
Competing interests ED has received consulting fees from Epi Excellence and Bohn Epidemiology. AA receives research support from the US Department of Defense (Army) (W81XWH-05-1-0117 (PI)) and the NIH (R01 NS045893 (PI), R01 NS047467 (PI), R01 NS48517 (PI), NINDS R01 NS042194 (PI) and R01 NS046635 (PI)).
Patient consent for publication Obtained.
Ethics approval This study was approved by the institutional review board of Brigham and Women’s Hospital.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement No data are available.